Purpose:Show what the inside of a laser looks like, and to show that the laser removes lots of spectral components from the light in the tube and only lets one wavelength out.
Description:The metal cover has been removed from a weak helium-neon laser, allowing the internal components to be seen, including the tube and the mirrors. Using a hand-held diffraction grating the light from in the tube can be seen to have a large number of spectral components. The light outside hits a white screen; looking at the spot with the grating shows that it is monochromatic, illustrating the lasing action.